<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            padding: 0;
            margin: 0;
        }
        html,body{
            width: 100%;
            height: 100%;
            /* 容器宽度高度都充满全屏 */
        }
        body{
            background-color: pink;
             display: flex;
             flex-direction: column;
             align-items: center;
             justify-content: center;

        }
        .a{
            width: 200px;
            height: 200px;
            background-color: red;
            position: relative;
            box-shadow: 0 0 30px red;
            transform: rotate(45deg)
            /* 顺时针旋转45° */
            
            
        }
        .a::before{
            content: "";
            width: 200px;
            height: 100px;
            background-color: red;
            position: absolute;
            left: 0;
            top: -99px;
            border-radius: 100px 100px 0 0;
            box-shadow: 0 0 30px red;
        }
        .a::after{
            content: "";
            width: 100px;
            height: 200px;
            background-color: red;
            position: absolute;
            left: -99px;
            top: 0;
            border-radius: 100px 0 0 100px;
            box-shadow: 0 0 10px red;
        } 
        @keyframes b{
            0%{
                background-color: red;
                transform: rotate(45deg) scale(0.6);
            }
            /* 25%{
                background-color: red;
                transform: rotate(45deg) scale(0.8);
            }
            50%{
                background-color: red;
                transform: rotate(45deg) scale(1);
            }
            75%{
                background-color: red;
                transform: rotate(45deg) scale(1.2);
            } */
            100%{
                background-color: red;
                transform: rotate(45deg) scale(1.4);
            }
        }
        .a{
            animation: b 1s linear 0s infinite  ;
        }
    </style>
</head>
<body>
    <div class="a"></div>
</body>
</html>